The present invention relates to a method and an apparatus for mixing of image signals, so as to obtain a printing master, in which an image is photoelectrically scanned, and reproduced in the form of the printing master.
The invention may be applied to color or monochrome scanners, to engraving machines, and to previewer devices, or the like. The signals include primary color-signals, color separation signals, and any form of correction signals.
The requirements which must be met will be illustrated using a color scanner by way of an example.
A color scanner serves to obtain corrected color records for multicolor printing. In order to obtain the color signals, the colored image to be reproduced, which is secured to a rotating scanning drum, is scanned point by point and line by line, by photoelectric scanning means. The color or chrominance signals, which represent the color components of the scanned image points, are fed to a color correction circuit, at the output at which there are available the color component signals determined according to the laws of subtractive color mixing, and if need be, a black separation signal and UCR signal for obtaining the color component signals, "magenta", "cyan", and "yellow", as well as a black separation signal. The color component signals are amplified and fed to a writing lamp, whose brightness is modulated by the associated color component signal. The process for obtaining an UCR-signal is known from U.S. Pat. No. 3,885,244 for example.
Films are secured to a rotatable recording drum, and are illuminated by the writing lamp point by point, and line by line.
The illuminated and developed films yield the desired color components for manufacturing a printing master for multicolored printing.
It will be understood that flat bed devices can be used as well. When using monochrome or color reproduction, it is sometimes required to superimpose two or several images, which is also denoted as "montage". For example, one image may contain an appropriate background, and another image, the foreground or a title. In general, such superimposition relates to showing in the reproduced copy certain image areas, or locally delineated regions of different images, either simultaneously or adjacent one another.
German Patent DT-DS No. 1,172,540, teaches a method in which the images to be combined are secured next to one another on a scanning drum, and are concurrently scanned by two scanners, respectively, to generate image signals. These image signals are alternately supplied to an electronic switch controlled by a control signal, and supplied therefrom to a writing lamp, which records desired combinations of images having relatively strongly delineated contours at the border region of the images.
But as the change of brightness of the writing lamp cannot follow without some inertia the image-signal step-function due to the switching-over process, there are reproduced frequently bright or dark edges, which have a very disturbing effect. In the known method a mask serves to control the switch, which contains the areas, or regions of the image areas adjacent one another, or the image components which blend, or are required to blend, within one another. This mask is scanned by means of a scanning means synchronously with the image, in order to obtain the control signal for the switch-over device, the scanning means including an input-storage device associated with the image to be scanned.
In order to avoid any disturbing edges in the reproduced image, the control mask must be matched very precisely to the image contours, or the image component contours, which in turn necessitates an expensive fabrication of the appropriate mask.
Undesired edges also arise, if the line-to-line scanning or reproduction is not sufficiently accurate with respect to the lines to be transferred.
It is the object of the present invention to avoid these disadvantages; this object is accomplished, if there occurs a continuous change of the image signal within a small zone of a border region of the areas to be scanned.
Smooth transitions are often desirable for editing reasons. Other reproducing requirements include the changing or correction of color or tonal gradations within locally defined regions.
For example, selective corrections may be required only within a certain region, or a region may have to be excluded from selective correction. Frequently, a tonal gradation correction is also required, when a transition occurs in the image from monochrome rendition to colored rendition. These regions can be defined by an appropriately formed color mask, or may be determined by color-selective switching circuits.
According to British Pat. No. 1,400,806, the border regions of the areas are also stored as position data in an X-Y recording system. During reproduction, the actual position and data of the scanner are compared with the storage position data.
In all known methods, the correction signals are switched in a step-wise manner, at the bordering areas.
But a smooth transition of the corrective control is frequently desired at the border regions of respective areas.
It is also desirable to actuate the various control circuits during monochrome or color reproduction within the signal paths of the image signals or color signals; the control then does not become effective during reproduction of the image in a step-wise manner, but acts continuously within a predetermined transition zone.